Multiple pregnancies are categorized as “high risk” for a reason. It’s not just a matter of the limited room in our womb squishing our babies up against each other. The human female body is optimized to gestate one baby. When you add in more, there’s a chance that not all resources will end up being distributed evenly.

If you’re new to How Do You Do It? and didn’t come here specifically to learn about sIUGR, I encourage you to read through the amazing birth stories on this site. The MoMs of HDYDI have experienced the full range of multiple pregnancy possibilities, from full-term to micropreemie, from extended bedrest to working right to the end, from natural childbirth to C-section. Don’t be scared by this one set of potential complications. Most of us have perfectly healthy and happy children today!

Meet Jenn

Meet Jenn, HDYDI‘s newest contributor. One of her twin daughters was diagnosed with Selective Intrauterine Growth Restriction. We’ll explain exactly what that is after Jenn tells her story.

My name is Jenn, and I’m a 32 year old mom of a sweet 4 year old boy and 5 month identical twin girls. This is my story about our experience with Selective Intrauterine Growth Restriction.

At 9 weeks pregnant, I found out we were expecting monozygotic/diamniotic (identical) twins. After the initial shock wore off (let’s be honest, I’m not sure the shock and wonder ever wear off!), I dove into books and the Internet to educate myself as much as possible as to what to expect for the next 7 months. I read about a million complications – preterm labour, how large I was going to get, and about Twin to Twin Transfusion Syndrome (TTTS).

Being a worrier to begin with, I began to go over all the things that could go wrong, but most of all, I feared my babies would be affected by TTTS. That fear became real at my 21 week OB appointment. After a fairly easy pregnancy to that point, my OB declared there was a problem. “They are identical, they should be the same size” he said. My Twin B was two weeks behind her sister in size.

“This isn’t good, I think you have TTTS”.

The next thing we knew, my OB was sending us four hours away to the top TTTS hospital in our province, and we were being prepared for surgery. My whole world caved in. I remember calling my mom in tears, telling her how I was so scared to lose my girls. I didn’t know what to think or do. When we arrived we were given an extensive ultrasound – over two hours long.

As we sat down to discuss the results with the doctor, he said that we had no signs of TTTS. I was confused. He then said our itty bitty Baby B had Selective Intrauterine Growth Restriction. What? I hadn’t read about that during my research.

He explained sIUGR is an issue that can arise only in pregnancies where the babies share a placenta. Then, he drew us a diagram showing us that Baby B had a marginal cord insertion, which means her umbilical cord wasn’t centrally located, instead being off to one side. This means she was only being supported by 25% of the placenta whereas her sister was getting the other 75%.

The doctor (who was a Maternal Fetal Medicine Specialist or MFM) said that I would need to be referred to my local MFM for weekly monitoring of growth and cord flow, but to expect a 36 week delivery by Caesarian section. The MFM also explained to me that many identical twins experience varying degrees of sIUGR due to cord placement, and that most sIUGR babies can catch up after birth.

I have to say I breathed a huge sigh of relief, considering we were expecting TTTS surgery that day. We headed home and started our weekly monitoring with my new MFM. He made sure to check UA umbilical artery (UA) and middle cerebral (MCA) artery dopplers, fluid levels, growth and bladder diameters at each ultrasound to stay on top of potential complications. At that point, we were watching UA cord flow to ensure it didn’t reverse, which would be cause for immediate delivery.

Every week was a rollercoaster. One week we would have intermittent/absent flow and our little would have only gained a few grams. Other weeks we had perfect cord flow and she was gaining beautifully. The most important thing I could hold on to was the advice I received on a Facebook support group for sIUGR/IUGR babies. I was advised that as long as there was SOME growth each week, and no reverse flow, we were okay.

I began to research more things I could do to help my babies grow. I read about a high protein diet so I made sure to take in as much as I could. Every week I either cried with worry, or felt cautiously optimistic.

Finally, as I approached 35 weeks, my sIUGR twin slowly stopped growing, and it was time to discuss induction. I had wanted to try for a VBAC, which my MFM was cautiously willing to try if I wanted to. However, after discussing the possible, and very real, risks involving a VBAC and my SIUGR twin, it was decided to schedule a C-section.

I made it to my scheduled date at 36.4 weeks, but oh, how I wished I could keep them in a little longer to grow a little bigger. When the MFM delivered my Twin A, she was a healthy weight of 5.6lbs. When my sIUGR twin was delivered, I remember the doctors saying how tiny she was, and the MFM said to me “I’m glad we got her out when we did”. She was 3.14lbs and the sweetest tiniest little pumpkin ever.

They whisked her off to the NICU, but assured me she was perfectly fine and would only be there 2-3 days max – she just needed to get her weight up before going home. She was alert, and nursing better than her “big” sister and we couldn’t wait to get them both home.

Unfortunately, she picked up a severe blood infection from an IV she received in the NICU, and her 3 day stay ended up being a scary 17 days full of close calls and a LOT of tears. Fast forward (and boy does time fast forward with babies) to today, where our sweet sIUGR twin Charlie is five months old. At three months, she was tipping the scales at over 11lbs, and her twin Addie was over 13lbs.

Charlie is perfect in every way, and although the doctors say she will likely always be “petite” she has overcome everything she’s been through like the little warrior she is. The smallest babies are always the fiercest. Charlie was followed by a dietician for the first two months of her life as she aimed to make her place on the growth charts, but she’s now above the 10th percentile and growing on her own perfect little curve.

We are very lucky.

sIUGR has many levels of severity, and our situation could have been much more difficult. Educating yourself is key. My OB didn’t know what it was and assumed it was TTTS. In fact, too many health professionals aren’t privy to the details of sIUGR and TTTS. I’m thankful to have been sent away for more testing, because ultimately I ended up being well taken care of by a MFM who knew what to look for and how to monitor a sIUGR pregnancy.

The number one thing I recommend to a mommy who has been diagnosed with sIUGR is to find a support group full of other moms who have been, or are going through, the same thing you are. They are often very knowledgable on what questions you should be asking and what kind of care you should be getting. I’m so thankful for those moms and the constant information and reassurance they offered.

There is nothing I did or didn’t do to cause sIUGR, and there was nothing I could do to fix or help the situation. That, of course, doesn’t help the guilt or helplessness you feel as a mommy. This is just another curveball in the crazy journey that is being a mom of multiples! Our babies aren’t the only warriors here after all!

What Is sIUGR?

Multiples and singletons alike, some babies are affected by a condition called intrauterine growth restriction (IUGR). This term describes a baby who is growing significantly slower than expected in the womb, one who is smaller than 90% of babies of the same gestational age (the time that has passed since conception). Causes of IUGR can be related to the placenta, through which the baby receives nutrition and oxygen, maternal health, or chromosomal issues. Selective intrauterine growth restriction (sIUGR) is a specific type of IUGR that only occurs in identical multiple pregnancies. The “selective” part means that not all babies’ regions of the placenta are impacted.

sIUGR occurs in about 10% of monochorionic pregnancies. Those of us with mono/mono or mono/di twins are at risk. (For more information on these terms and general information about twin pregnancies, please see our primer.) In sIUGR, one twin is getting so little of his or her share of the placenta that it is impacting growth. To be blunt, that twin is malnourished and possibly under-oxygenated. This is particularly obvious when comparing the sIUGR twin to his or her wombmate, who, all things being equal, should be about the same size.

MoMs, we are masters of guilt. If your baby has been diagnosed with sIUGR, it is not your fault. These things just happen. The fact that you have a diagnosis means that you’re doing what you should for your children. You’re getting regular medical care. Your doctors can help get your baby healthy.

How Does sIUGR Develop?

Background

Let’s make sure we’re all familiar with the basic terms.

Let’s now look more closely at the placenta. The placenta is your babies’ anchor and food source. It is the place where mom’s cells and babies’ cells meet. Mom’s blood vessels bring in her oxygenated and nutrition-laden blood, which transfer their goodies to babies’ blood in babies’ blood vessels. On the way out, Mom’s blood picks up babies’ waste so that her body can get rid of it for them.

Umbilical Cord Insertion

Ideally, the umbilical cord attaches to the placenta near its center, allowing plenty of room for blood vessels to spread out and maximize the connections between Mom and baby. However, this becomes more complicated when there’s more that one umbilical attaching to a shared placenta.

In most cases, as with Sadia’s daughters, each twin’s umbilical cord is close enough to the middle to claim plenty of placental real estate for his or her blood vessels. Complications can arise when the placenta is shared unevenly.

sIUGR and TTTS

In rare cases, as with Jenn’s daughters, one umbilical cord attaches off to the side and doesn’t get its fair share. The other umbilical cord’s placement is still optimal. Only the undernourished baby is negatively affected, his or her growth limited by the nutrition making it through. This is sIUGR, a condition often initially misdiagnosed as TTTS.

In about 15% of twins who share a placenta, one twin gets far more than his or her share of the placenta while the other gets far less. This is called Twin-to-Twin Transfusion syndrome, or TTTS. In effect, the donor twin is giving a transfusion of the blood to the recipient twin. One baby ends up overfed and the other undernourished, which is dangerous for both babies.

An initial diagnosis of TTTS may be modified to one of sIUGR if observation of the possible donor twin finds that there’s nothing to be concerned about when it comes to cord insertion.

Surgery

TTTS surgery involves using a laser to block blood vessels carrying blood between the twins. Its benefit is primarily to the twin who is receiving too much blood. Medicine has not yet advanced to the point where surgery is available to make a greater blood supply available to the donor twin or to a baby diagnosed with sIUGR. Frequent ultrasound monitoring is the only real option, allowing your doctor to determine whether it’s safer for your babies to be delivered pre-term than to continue to be nourished in utero by the placenta.

If you have any questions about sIUGR or TTTS, please let us know. We’ll do our best to answer, although neither of us is a medical professional. You can find out much more about TTTS on the TTTS Foundation website.

As if we needed any proof that our multiples are miracles, National Geographic has a wonderful documentary about the life of multiples in utero. See 4D ultrasound of siblings interacting before they’re even born.

The In the Womb series also includes a video entirely about identical twins in the womb, which we just loved. Do be aware that there’s a scene in both films with a silhouette of the act of conception that you may want to skip through if you haven’t had The Talk yet. There are also diagrams of male and female anatomy. You may want to watch it all the way through without kids at least once.

My Story

I was 7 weeks pregnant when I had my first ultrasound. The doctor pointed out the shared outer sac (chorion) and the two distinct inner sacs (amnions). I didn’t need her to finish. Thanks to Advanced Placement Bio class in high school (embryonic development) I knew I had a miracle in my womb: identical twins. Once we’d called everyone we needed to share the good news with, I hit Google, and quickly concluded from their monochorionic/diamniotic (mono/di) state that my little ones had split from a single cluster of identical cells somewhere between 3 and 9 days after conception. I’ll tell you how I made the calculation in a little bit.

The Basics

Most people don’t know a whole lot about twins or higher order multiples, and are intrigued by them. Folks I run into are usually aware that there are two basic types, identical and fraternal, but often don’t know precisely what the difference is. Part of this comes from the term “identical.” In casual English, “identical” means “exactly the same,” and so people often assume that identical twins should look alike, act alike, and think alike. This assumption often gets extended to fraternal twins, in that they should look different, act differently, and think differently.

I don’t argue with people about whether my children look enough alike to be “really” identical, and instead give them a quick science lesson. You’d be surprised how many medical professionals, even obstetricians, don’t remember the science of twinning they covered in the depths of college or medical school, and therefore jump to possibly incorrect conclusions about whether a set of twins is identical or fraternal. Next time you need to explain the distinction to someone, feel free to use the visual aids below.

The Science

Identical multiples grow from the same fertilized egg and therefore have basically the same DNA. Fraternal multiples come from different fertilized eggs, and therefore basically share 50% of the same DNA, as do siblings conceived by the same parents at different times. Sharing a DNA template makes it likely that identical siblings will look very much alike, but DNA doesn’t predict everything.

My daughters, for instance, share their DNA, but have noses of different shapes and different hairlines, due to developmental differences that don’t appear to have a genetic basis. They’re also different heights, likely because one is a pickier eater than the other and because dysphagia related to macroglossia (trouble swallowing because her tongue was too big for her mouth) meant that she ate less than Sissy after she weaned.

Vocabulary

Before I go much further into the science, let’s talk about the terminology we’ve been using.

So, the embryo is inside the amnion, which is in turn inside the chorion. The umbilical cord traverses the two membranes to connect the embryo to the placenta, which collects nutrition from mommy for baby.

Twins in the Womb

Now let’s talk twins.

Monozygotic twins are identical ones. They started from a single zygote. (Mono means one.) Dizygotic twins are fraternal ones. They started from two zygotes. (Di means two.)

Monochorionic/monoamniotic (mono/mono) twins are monozygotic twins who share a single amnion and a single chorion.

Monochorionic/diamniotic (mono/di) twins, like my daughters, are monozygotic twins who have separate amnions and share a single chorion.

Dichorionic/diamniotic (di/di) twins are monozygotic or dizygotic twins who have separate amnions and separate chorions.

I try to make this clearer in the image below. With one egg and sperm, you can get one baby… or two babies who are mono/mono, mono/di or di/di. With two eggs and two sperm, you’ll always get di/di twins.

So here’s the trick. In the image above, you can’t tell the difference between the identical di/di twins and the fraternal di/di twins. And neither can the ultrasound tech. So, if you have di/di twins, chances are good that they’re fraternal, but you just don’t know for sure.

Reader Noura I was kind enough to share ultrasound images of her di/di identical twins, whose ultrasounds look just like those of fraternal twins. Remember, the mono-di stuff refers to the membranes around the babies, and not the numbers of eggs and sperm.

Reading the Ultrasound

So, in my little chart above, I had to note that there are extraordinarily rare cases of boy/girl identical twins, but this is a teeny tiny proportion of the population. If you ran across such a pair, you’d recognize them from the news. So, please, just assume that boy/girl twins are fraternal (dizygotic) or that one had a sex change. Either way, it’s not polite to ask. Girl/girl twins and boy/boy twins can be fraternal or identical.

Timing of Monozygotic Twin Split

Here’s a fun fact. The arrangement of amnion and chorion can tell those of us with identical twins when they split apart!

TTTS can be very serious and put both your babies at risk. The placental blood supply is shared unevenly, meaning that one has more than his or her share of nutrition and oxygen, the other less than his or hers. Many obstetricians will closely monitor mothers expecting twins to watch for TTTS. While it’s almost unheard of with fraternal twins, reader Halie H. wrote to us to say, “My di/di fraternal (boy/girl) twins’ placentas fused. They were born with one failed and one really really red placenta; they were sent off to be studied as an example of TTTS in fraternals.”

I’m not an expert on this stuff, but I do love genetics and studied it in college (although I ended up switching away from a biology major junior year). If you have additional questions, I’ll do my best to answer them.

Before I sign off, I need to give a big old shout out to Canva.com. I have been planning to write this post for years, but not having an artistic bone in my body, knew that I couldn’t do it justice without an illustrator. Thanks to the free online graphic design tool, Canva, I was able to create the graphics I’ve included in this post.

They do not look the same. This weekend, we went to a knitting class for kids in Austin. The other mom there asked which of the girls was mine; she had assumed that they were friends whom I’d brought to class together.

People frequently ask me how my girls can possibly be identical if they don’t look the same. After all, don’t they belie the very definition of identical? The same question was asked by another mother of identical twins in a MoM Facebook group recently. She wondered how it was that only one of her twins had crossed eyes so severe that he needed surgery. Shouldn’t both have the crossed eyes if one did? As you may know, M has a condition called frontonasal dysplasia that impacts how she looks. J doesn’t have this condition. I felt compelled to answer the other mom’s question, then realized my response to the other mom was worth sharing with you.

The confusion comes from the usage of the word identical. Used colloquially, it means that two things are alike in all ways. Used scientifically to describe two organisms, it means only that they share their genetic makeup. My daughters’ DNA is identical (more or less; every time a cell divides in two, there’s the potential for something to get miscopied, resulting in a minute genetic change). That’s what makes them “identical” twins. Personally, I prefer the term monozygotic to identical. It makes clear that my daughters started as a single (mono) fertilized egg (zygote).

DNA doesn’t dictate everything. In the case of my girls, the sides of J’s face came together exactly on schedule, so she’s symmetrical . M’s facial formation was behind schedule for some reason we don’t know, so she has a cleft running down the center of her face and an adorably unusual nose. Even though they can look very similar, their noses, foreheads and chins are different. Plus, J has a dimple, an interruption in her cheek muscle, that M doesn’t.

My M also had amblyopia. Essentially, her brain ignored the message from her left eye, rendering her functionally blind in that eye. We caught it early, and we were able to resolve it by having her wear a patch over her “good” eye several hours a day for a few months. Her twin J has always had perfect vision in both eyes.

The biology of differences between identicals can be pretty complex, but think of it this way. The DNA that our identical kids share is the blueprint from which they are built. However, the actual process of fetal development (just like house construction) introduces teeny tiny differences. When those differences comes early in development (think during the framing of a house) they can have a really major impact on the final product, whether human or house.

Especially when our kids have medical challenges, it’s really easy to blame ourselves and wonder if there’s something we as moms could have done differently. There usually isn’t.

And really, would I want my kids to be exactly alike? M’s sparkling wit is a foil for J’s earnestness. J’s emotional maturity balances M’s academic precocity. M’s musical and artistic ability are a match for J’s literary talents.

My unique girls are not identical people even though their matching DNA makes them identical twins.

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